Thermal compress bonding

ABSTRACT

A method includes providing a substrate carrier including work piece holders, and placing a first plurality of work pieces into the work piece holders. A second plurality of work pieces is picked up and placed, with each of the second plurality of work pieces being placed on one of the first plurality of work pieces. Solder bumps between the first and the second plurality of work pieces are then reflowed to simultaneously bond the first and the second plurality of work pieces together.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of U.S.patent application Ser. No. 12/841,858, filed on Jul. 22, 2010, now U.S.Pat. No. 8,381,965, entitled “Thermal Compress Bonding,” which is herebyincorporated herein in its entirety by reference.

TECHNICAL FIELD

This disclosure relates generally to integrated circuit manufacturingprocesses, and more particularly to thermal compress bonding.

BACKGROUND

Integrated circuits are formed on semiconductor wafers, which are thensawed into semiconductor chips. The semiconductor chips are then bondedonto package substrates. FIGS. 1 through 3 illustrate cross-sectionalviews of intermediate stages in a conventional bonding process.Referring to FIG. 1, package substrate 100 is provided, and bond pads108 are at the surface of package substrate 100. Chip 102 is picked upand flipped over, with solder bumps 104 at a surface of chip 102 facingdown. Flux 106 is also applied on solder bumps 104.

Next, as shown in FIG. 2, chip 102 is placed on package substrate 100,with solder bumps 104 being placed against bond pads 108. Packagesubstrate 100 and chip 102 then go through a reflow process, duringwhich package substrate 100 and chip 102, and solder bumps 104 areheated. The resulting bonded structure is shown in FIG. 3. Due to theweight of chip 102 and solder bumps 104, solder bumps 104, when melted,are collapsed, and width W1 of solder bumps 104 increases.

One of the problems found in the conventional bond structures is thatcracking often occurs in solder bumps 104 after the bonding process,particularly near wherein solder bumps 104 join solder resists 112 andpassivation layer (or polyimide layer) 114. In addition, due to theincrease in width W1 of solder bumps 104, the spacing betweenneighboring solder bumps 104 decreases, causing greater risk of shortingbumps 104 to each other.

SUMMARY

In accordance with one aspect, a method includes providing a substratecarrier including work piece holders, and placing a first plurality ofwork pieces into the work piece holders. A second plurality of workpieces is picked up and placed, with each of the second plurality ofwork pieces being placed on one of the first plurality of work pieces.Solder bumps between the first and the second plurality of work piecesare then reflowed to simultaneously bond the first and the secondplurality of work pieces together.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 3 illustrate cross-sectional views of intermediatestages in a conventional bonding process;

FIG. 4A illustrates a top view of a substrate carrier; and

FIGS. 4B through 7 illustrate cross-sectional views of intermediatestages in a thermal compress bonding (TCB) process in accordance withvarious embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A novel thermal compression bonding (TCB) process is provided. Theintermediate stages of manufacturing various embodiments areillustrated. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

FIGS. 4A and 4B illustrate a top view and a cross-sectional view,respectively, of substrate carrier 20. Substrate carrier 20 includes aplurality of work piece holders 22, which may be arranged as an arrayhaving rows and columns. As shown in FIG. 4B, work piece holders 22 maybe holes having the size of work pieces 26 (not shown in FIGS. 4A and4B, please refer to FIG. 5) that will be placed therein. In anembodiment, heater 24 is placed under, or built in, substrate carrier 20for heating the work pieces placed in work piece holders 22. Inalternative embodiments, substrate carrier 20 includes no heater.

Referring to FIG. 5, work pieces 26 are placed into work piece holders22. In an embodiment, work pieces 26 are package substrates orinterposers, which do not have active devices such as transistorstherein. In alternative embodiments, work pieces 26 are device dieshaving active devices such as transistors (not shown) therein. Metalbumps 28 are formed on top surfaces of work pieces 26. In an embodiment,all work piece holders 22 are filled with work pieces 26. Alternatively,a part, by not all, of work pieces holders 22 is filled.

Next, as shown in FIGS. 6A and 6B, work pieces 30 are picked up andplaced onto work pieces 26. Metal bumps 32 at bottom surfaces of workpieces 30 are in contact with metal bumps 28. Work pieces 30 may bedevice dies (chips) comprising active devices (not shown), which may betransistors. Alternatively, work pieces 30 may be interposers, packagesubstrates, or the like. In an embodiment, metal bumps 32 are solderbumps, although they can be other type of bumps such as copper bumps.However, at least one, and may be both, of metal bumps 28 and 32 aresolder bumps. In the following illustrated exemplary embodiments, metalbumps 28 and 32 are all solder bumps.

Heating tool 36 is placed over and contacting work pieces 30, and mayapply a downward force (symbolized by arrow 39) on work pieces 30, sothat metal bumps 28 and 32 are pressed against each other to preventwork pieces 30 from slipping. In FIG. 6A, heating tool 36 includes aplurality of heating heads 38. When placed over work pieces 30, each ofheating heads 38 is aligned to, and contacts, one of work pieces 30. InFIG. 6B, heating tool 36 includes only one heating head that has a sizegreat enough to contact all of work pieces 30.

Next, as shown in FIG. 7, a bonding is performed. Heating tool 36 heatswork pieces 30, and the heat is conducted to, and causing the reflow of,solder bumps 28 and 32. The resulting solder bumps formed of combinedsolder bumps 28 and 32 are referred to as solder bumps 40. In theembodiment as shown in FIG. 6A, all heating heads 38 are at a sametemperature, and hence all of solder bumps 28 and 32 are melted. In theembodiment as shown in FIG. 6B, the surface portions of heating head 38contacting different work pieces 30 have a substantially uniformtemperature, and hence all of solder bumps 28 and 32 are meltedsubstantially simultaneously. During the melting of solder bumps 28 and32, heating tool 36 (and work pieces 30) may be kept at a fixed level toprevent the melted bumps 28 and 32 from further collapse, which mayfurther cause neighboring bumps 28/32 to short to each other. After thereflow to form solder bumps 40, heating tool 36 applies an upward force,as symbolized by arrow 42, so that heights H of solder bumps 40 areincreased, and horizontal sizes W2 of solder bumps 40 are reduced. Theapplication of the upward force may be achieved, for example, bycreating a vacuum in heating tool 36 to suck work pieces 30 up, whereinthe vacuum may be generated in pipes 31. During the reflow process,heater 24 may have an elevated temperature to heat work pieces 26.Alternatively, heater 24 is not heated. The temperature of heating tool36 is then lowered until solder bumps 40 solidify. The bonding processis then finished.

In the embodiments shown in FIGS. 4A through 7, all work pieces onsubstrate carrier 20 are bonded simultaneously. In alternativeembodiments, substrate carrier 20 may be divided into a plurality ofzones, with each zone including a plurality of work piece holders 22.The plurality of work pieces in a same zone my be bonded simultaneouslyusing essentially the same methods as shown in FIGS. 4A through 7, whilethe work pieces in different zones may be bonded in different periods oftime.

By using the embodiments, the throughput of the bonding process issignificantly improved. For example, assuming ten chips are to be bondedto ten package substrates, and only one chip is bonded each time. Thepicking and placing of each chip takes 2 seconds, and the heating andreflowing of each chip takes 30 seconds. The total time required forbonding all 10 chips will be (2+30)×10, which is 320 seconds. As acomparison, by using the embodiments, although the picking and placingof ten chips still take 20 seconds in total, the heating and reflowingof ten chips only take 30 seconds due to the simultaneously reflowing ofall chips. The total time is thus only 50 seconds. If more chips arebonded simultaneously, the improvement in the throughput is moresignificant. Since the cost of the TCB bonding is very high, thereduction in the cost of the bonding process due to the improvedthroughput is also significant.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: placing a first plurality ofwork pieces into work piece holders of a substrate carrier; picking upand placing a second plurality of work pieces, with each of the secondplurality of work pieces being placed on corresponding ones of the firstplurality of work pieces; bringing the first plurality of work pieces incontact with a first heating tool, wherein the first heating tool isintegral with the substrate carrier; heating the first plurality of workpieces with the first heating tool; bringing the second plurality ofwork pieces in contact with a second heating tool and heating the secondplurality of work pieces with the second heating tool, the secondheating tool being configured to apply a force on the second pluralityof work pieces and being different than the first heating tool; andreflowing a first plurality of solder bumps between the first and thesecond plurality of work pieces to form a second plurality of solderbumps and bond the first and the second plurality of work piecestogether.
 2. The method of claim 1, wherein the second heating toolcomprises a plurality of heating heads.
 3. The method of claim 1,wherein the second heating tool comprises a single heating headcontacting each of the second plurality of work pieces.
 4. The method ofclaim 1 further comprising: before the step of reflowing, applying adownward force to press the second plurality of work pieces against thefirst plurality of work pieces; during the step of reflowing, holdingthe second plurality of work pieces at a fixed level; and after thefirst plurality of solder bumps are melted, applying an upward force tothe second plurality of work pieces to increase heights of the secondplurality of solder bumps before the second plurality solder bumps aresolidified.
 5. The method of claim 1, wherein the first and the secondplurality of work pieces are arranged in an array.
 6. The method ofclaim 1, wherein the first plurality of work pieces fill all work pieceholders in the substrate carrier.
 7. The method of claim 1, wherein thefirst plurality of work pieces are package substrates, and the secondplurality of work pieces are device dies.
 8. The method of claim 1,wherein the first plurality of solder bumps are on the first pluralityof work pieces.
 9. The method of claim 1, wherein the first plurality ofsolder bumps are on the second plurality of work pieces.
 10. The methodof claim 1, wherein at least one of the first and second plurality ofwork pieces comprises a plurality of metal bumps.
 11. A methodcomprising: placing a first plurality of work pieces into work pieceholders of a substrate carrier; picking up and placing a secondplurality of work pieces, with each of the second plurality of workpieces being vertically aligned to corresponding ones of the firstplurality of work pieces, wherein one of the first and second pluralityof work pieces comprises a first plurality of solder bumps; placing afirst heating tool in contact with the first plurality of work pieces,the first heating tool being integral with the substrate carrier;placing a second heating tool over and contacting the second pluralityof work pieces; heating the first plurality of work pieces using thefirst heating tool and heating the second plurality of work pieces usingthe second heating tool to perform a reflow process, wherein the firstplurality of solder bumps are melted to form a second plurality ofsolder bumps; and before the second plurality of solder bumps issolidified, simultaneously applying an upward force to the secondplurality of work pieces to increase a height of the second plurality ofsolder bumps.
 12. The method of claim 11, wherein the second heatingtool comprises a plurality of heating heads.
 13. The method of claim 11,wherein the second heating tool comprises a single heating headcontacting all of the second plurality of work pieces.
 14. The method ofclaim 11 further comprising, before and during the step of reflowing,applying a downward force to press the second plurality of work piecestoward the first plurality of work pieces.
 15. The method of claim 11,wherein the first and the second plurality of work pieces are arrangedin an array.
 16. The method of claim 11, wherein the first plurality ofwork pieces fill all work piece holders in the substrate carrier. 17.The method of claim 11, wherein the first plurality of work pieces arepackage substrates, and the second plurality of work pieces are devicedies.
 18. The method of claim 11, wherein the other of the first andsecond plurality of work pieces comprises metal bumps.
 19. The method ofclaim 11, wherein the first plurality of solder bumps are on the firstplurality of work pieces.
 20. The method of claim 11, wherein the firstplurality of solder bumps are on the second plurality of work pieces.